This application is a continuation-in-part of application Ser. No. 09/612,572, filed on Jul. 7, 2000 now abandoned, and a continuation-in-part of application Ser. No. 09/767,940, filed on Jan. 24, 2001 now abandoned, the disclosures of which are incorporated herein by reference.
This invention relates to unleaded motor fuel for spark ignition internal combustion engines. More particularly the invention relates to a method for lowering the dry vapor pressure equivalent (DVPE) of a fuel composition including a hydrocarbon liquid and ethanol by using an oxygen-containing compounds and C6-C12 hydrocarbons. The ethanol and DVPE adjusting components used to obtain the fuel composition are preferably derived from renewable raw materials. By means of the method of the invention motor fuels containing up to 20% by volume of ethanol meeting standard requirements for spark ignition internal combustion engines operating with gasoline are obtainable.
Conventional gasoline (xe2x80x9cgasolinexe2x80x9d) is the major fuel for spark ignition internal combustion engines. As employed herein, the phrase conventional gasoline includes a volatile, highly inflammable, generally colorless, liquid obtained by fractional distillation of petroleum. The extensive use of gasoline results in the pollution of the environment. The combustion of gasoline derived from crude oil or mineral gas disturbs the carbon dioxide balance in the atmosphere, and causes the greenhouse effect. Crude oil reserves are decreasing steadily with some countries already facing crude oil shortages.
The growing concern for the protection of the environment, tighter requirements governing the content of harmful components in exhaust emissions, and crude oil shortages, force industry to develop urgently alternative fuels which burn more cleanly.
The existing global inventory of vehicles and machinery operating with spark ignition internal combustion engines does not allow currently the complete elimination of gasoline as a motor fuel.
The task of creating alternative fuels for internal combustion engines has existed for a long time and a large number of attempts have been made to use renewable resources for yielding motor fuel components.
U.S. Pat. No. 2,365,009, issued in 1944 describes the combination of C1-C5 alcohols and C3-C5 hydrocarbons for use as a fuel. In U.S. Pat. No. 4,818,250 issued in 1989 it is proposed to use limonene obtained from citrus and other plants as a motor fuel, or as a component in blends with gasoline. In U.S. Pat. No. 5,607,486 issued in 1997, there are disclosed novel engine fuel additives comprising terpenes, aliphatic hydrocarbons and lower alcohols.
Currently tert-butyl ethers are widely used as components of gasolines. Motor fuels comprising tert-butyl ethers are described in U.S. Pat. No. 4,468,233 issued in 1984. The major portion of these ethers is obtained from petroleum refining, but can equally be produced from renewable resources.
Ethanol is a most promising product for use as a motor fuel component in mixtures with gasoline. Ethanol is obtained from the processing of renewable raw material, known generically as biomass, which, in turn, is derived from carbon dioxide under the influence of solar energy.
The combustion of ethanol produces significantly less harmful substances in comparison to the combustion of gasoline. However, the use of a motor fuel principally containing ethanol requires specially designed engines. At the same time spark ignition internal combustion engines normally operating on gasoline can be operated with a motor fuel comprising a mixture of gasoline and not more than about 10% by volume of ethanol. Such a mixture of gasoline and ethanol is presently sold in the United States as gasohol. Current European regulations concerning gasolines allow the addition to gasoline of up to 5% by volume of ethanol.
The major disadvantage of mixtures of ethanol and conventional gasoline is that for mixtures containing up to about 20% by volume of ethanol there is an increase in the dry vapor pressure equivalent as compared to that of the conventional gasoline.
FIG. 1 shows the behavior of the dry vapor pressure equivalent (DVPE) as a function of the ethanol content of mixtures of ethanol and gasoline A92 summer, and gasoline A95 summer and winter at 37.8xc2x0 C. The gasolines known as A92 and A95 are standard, conventional gasolines purchased at gas stations in the United States and Sweden. Gasoline A92 originated in the United States and gasoline A95, in Sweden. The ethanol employed was fuel grade ethanol produced by Williams, USA. The DVPE of the mixtures was determined according to the standard ASTM D-5191 method at the SGS laboratory in Stockholm, Sweden.
For the range of concentrations by volume of ethanol between 5 and 10% which is of particular interest for use as a motor fuel for standard spark ignition engines, the data in FIG. 1 show that the DVPE of mixtures of gasoline and ethanol can exceed the DVPE of source gasoline by more than 10%. Since the commercial petroleum companies normally supply the market with gasoline already at the maximum allowed DVPE, which is strictly limited by current regulations, the addition of ethanol to such presently commercially available gasolines is not possible.
It is known that the DVPE of mixtures of gasoline and ethanol can be adjusted. U.S. Pat. No. 5,015,356 granted on May 14, 1991 proposes reformulating gasoline by removing both the volatile and non-volatile components from C4-C12 gasoline to yield either C6-C9 or C6-C10 intermediate gasoline. Such fuels are said to better facilitate the addition of alcohol over current gasoline because of their lower dry vapor pressure equivalent (DVPE). A disadvantage of this method of adjusting the DVPE of mixtures of gasoline and ethanol is that in order to obtain such a mixture it is necessary to produce a special reformulated gasoline, which adversely affects the supply chain and results in increased prices for the motor fuel. Also, such gasolines and their mixtures with ethanol have a higher flash point, which impairs their performance properties.
It is known that some chemical components decrease DVPE when added to gasoline or to a mixture thereof with ethanol. For example, U.S. Pat. No. 5,433,756 granted on Jul. 18, 1995 discloses chemical clean-combustion-promoter compounds comprising, in addition to gasoline, ketones, nitro-paraffin and also alcohols other than ethanol. It is noted that the composition of the catalytic clean-combustion-promoter disclosed in the patent reduces the DVPE of gasoline fuel. Nothing is mentioned in this patent about the impact of the clean-combustion-promoter composition on the DVPE of mixtures of gasoline and ethanol.
U.S. Pat. No. 5,688,295 granted on Nov. 18, 1997 provides a chemical compound as an additive to gasoline or as a fuel for standard gasoline engines. In accordance with the invention, an alcohol-based fuel additive is proposed. The fuel additive comprises from 20-70% alcohol, from 2.5-20% ketone and ether, from 0.03-20% aliphatic and silicon compounds, from 5-20% toluene and from 4-45% mineral spirits. The alcohol is methanol or ethanol. It is noted in the patent that the additive improves gasoline quality and specifically decreases DVPE. The disadvantages of this method of motor fuel DVPE adjustment are that there is a need for large quantities of the additive, namely, not less than 15% by volume of the mixture; and the use of silicon compounds, which form silicon oxide upon combustion, results in increased engine wear.
In WO9743356 a method for lowering the vapor pressure of a hydrocarbon-alcohol blend by adding a co-solvent for the hydrocarbon and alcohol to the blend, is described. A spark ignition motor fuel composition is also disclosed, including a hydrocarbon component of C5-C8 straight-chained or branched alkanes, essentially free of olefins, aromatics, benzene and sulphur, in which the hydrocarbon component has a minimum anti-knock index of 65, according to ASTM D-2699 and D-2700 and a maximum DVPE of 15 psi, according to ASTM D-5191; a fuel grade alcohol; and a co-solvent for the hydrocarbon component and alcohol in which the components of the fuel composition are present in amounts selected to provide a motor fuel with a minimum anti-knock index of 87 and a maximum DVPE of 15 psi. The co-solvent used is biomass-derived 2-methyltetrahydrofuran (MTHF) and other heterocyclic ethers such as pyrans and oxepans, MTHF being preferred.
The disadvantages of this method for adjusting the dry vapor pressure equivalent of mixtures of hydrocarbon liquid and ethanol are the following:
(1) It is necessary to use only hydrocarbon components C5-C8 which are straight-chained or branched alkanes (i) free of such unsaturated compounds as olefins, benzene and other aromatics, (ii) free of sulphur and, as follows from the description of the invention, (iii) the hydrocarbon component is a coal gas condensate or natural gas condensate;
(2) It is necessary to use as a co-solvent for the hydrocarbon component and ethanol only one particular class of chemical compounds containing oxygen; namely, ethers, including short-chained and heterocyclic ethers;
(3) It is necessary to use a large quantity of ethanol in the fuel, not less than 25%;
(4) It is necessary to use a large quantity of co-solvent, not less than 20%, of 2-methyltetrahydrofuran; and
(5) It is required to modify the spark ignition internal combustion engine when operating with such fuel composition and, specifically, one must change the software of the on-board computer or replace the on-board computer itself.
The article by D. Zudkevitch et. al. entitled xe2x80x9cThermodynamics of Reformulated Automotive Fuelsxe2x80x9d (Hydrocarbon Processing, vol. 76, no. 6, 1995) discloses compositions of the ethanol-containing gasolines, which also contain tert-butyl alcohol ethers. The presence of the latter results in a reduction of the vapor pressure, compared to the vapor pressure of the ethanol-containing gasoline. However, the vapor pressure of the three-component mixture is higher than the vapor pressure of the gasoline, which is one of the components of the mixture. Therefore, to achieve the vapor pressure of standard gasolines, these gasolines should be reformulated.
The reduction in the vapor pressure of a three-component mixture can also be achieved by adding to the fuel composition considerable amounts of the oxygen-containing compounds. However, the increased oxygen content in the fuel would worsen performance of a standard spark ignition combustion engine due to a decrease in the heat of combustion of such fuel.
Accordingly, one of the objects of the present invention is to provide a method by which the above-mentioned drawbacks of the prior art can be overcome. It is a primary object of the invention to provide a method of reducing the vapor pressure of a C3 to C12 hydrocarbon based fuel mixture containing up to 20% by volume of ethanol for conventional gasoline engines so that it is not more than the vapor pressure of the C3 to C12 hydrocarbon itself, or at least so that it meets the standard requirements for gasoline fuel.
The above-mentioned objects of the present invention have been accomplished by means of the method comprising combining:
(a) a hydrocarbon component comprising C3 to C12 hydrocarbon fractions;
(b) an ethanol component comprising fuel grade ethanol, said ethanol component comprising 0.1% to 20% of the composition by volume;
(c) an oxygen-containing component comprising at least one of (1) an alkanol having from 3 to 10 carbon atoms; (2) a ketone having from 4 to 9 carbon atoms; (3) a dialkyl ether having from 6 to 10 carbon atoms; (4) an alkyl ester of an alkanoic acid, said alkyl ester having 5 to 8 carbon atoms; (5) a hydroxyketone having 4 to 6 carbon atoms; (6) a keto ester of an alkanoic acid, said keto ester having 5 to 8 carbon atoms or (7) an oxygen-containing heterocyclic compound having 5 to 8 carbon atoms selected from the group consisting of tetrahydrofurfuryl alcohol, tetrahydrofurfuryl acetate, dimethyltetrahydrofuran, tetramethyltetrahydrofuran, methyl tetrahydropyran, 4-methyl-4-oxytetrahydropyran, and mixtures thereof, and said oxygen-containing additive comprises 0.05% to 15% of the total volume of the motor fuel composition; and
(d) at least one C6-C12 hydrocarbon,
This fuel composition comprises not more than 0.25% by weight of water according to ASTM D 6304 and not more than 7% by weight of oxygen according to ASTM D 4815. A ratio between components (b)/{(c)+(d)} is from 1:200 to 200:1 by volume.
The present inventors have found that specific types of compounds having an oxygen-containing group surprisingly lower the vapor pressure of a gasoline-ethanol mixture.
They have also found that the octane number of the resulting hydrocarbon based fuel mixture can surprisingly be maintained or even increased by using the oxygen-component of the present invention in combination with C6-C12 hydrocarbons.
According to the present method, up to about 20% by volume of fuel grade ethanol (b) can be used in the overall fuel compositions. The oxygen-containing compounds (c) used can be obtained from renewable raw materials, and the hydrocarbon component (a) used can for example be any standard gasoline (which does not have to be reformulated) and can optionally contain aromatic fractions and sulphur, and also hydrocarbons obtained from renewable raw materials.
By means of the method of the invention fuels for standard spark ignition internal combustion engines can be prepared, which fuels allow such engines to have the same maximum performance as when operated on standard gasoline currently on the market. A decrease in the level of toxic emissions in the exhaust and a decrease in the fuel consumption can also be obtained by using the method of the invention.
According to one aspect of the invention, in addition to the dry vapor pressure equivalent (DVPE), the anti-knock index (octane number) can also be desirably controlled. The octane number can be at least the same as that of the hydrocarbon component (a) or meet mandatory regulation limits for octane numbers without employing organo-metallic anti-knock additives.
It is yet another object to provide an additive mixture of fuel grade ethanol (b) and oxygen-containing additive (c) and an additional component (d), in which component (d) comprises at least one C6-C12 hydrocarbon and is present in an amount up to 99% by volume. This mixture can then be subsequently used in the method of the present invention, i.e., added to the hydrocarbon component (a).
The mixture of (b), (c) and (d) can also be used per se as a fuel for modified engines, i.e., not standard-type gasoline engines. The additive mixture can also be used for adjusting the octane number and/or for lowering the vapor pressure of a high vapor pressure hydrocarbon component.
Further objects and advantages of the present invention will be evident from the following detailed description, examples and dependent claims.